Posterior Compartment Mass

Robert B. Carr, MD

DIFFERENTIAL DIAGNOSIS

Common

Nerve Sheath Tumor
Sympathetic Ganglion Tumor
Lymphoma
Hiatal Hernia
Esophageal Tumor

Less Common

Metastasis
Foregut Duplication Cyst
Extramedullary Hematopoiesis
Aortic Aneurysm
Esophageal Varices
Spine Mass

Rare but Important

Hemangioma
Lymphangioma
Meningocele

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Anatomy of posterior compartment
- Description is based upon radiographic landmarks
  - Anterior border: Line 1 cm behind anterior margin of thoracic vertebrae
  - Posterior border: Chest wall
Normal contents: Vertebral bodies, descending aorta, azygos vein, esophagus, lymph nodes, adipose tissue
Cervicothoracic sign: Mediastinal mass outlined by lung on frontal radiograph above level of clavicle; indicates posterior location
CT and MR are invaluable for determining site of origin and tissue characterization

Helpful Clues for Common Diagnoses

Nerve Sheath Tumor
- More common in adults
- Schwannoma, neurofibroma, plexiform neurofibroma
- Smooth, round or oval, often less dense than muscle
- Enlargement of adjacent neural foramina with occasional extension into spinal canal
- Often have internal foci of decreased attenuation due to lipid or cyst formation
- Increased signal on T2 MR images and heterogeneous enhancement
Sympathetic Ganglion Tumor
- More common in children and young adults
- Ganglioneuroma
  - Benign neoplasm of ganglion cells and Schwann cells
  - Most common in 2nd and 3rd decades
  - Calcification in 20%
  - May have whorled appearance on MR
- Ganglioneuroblastoma
  - Intermediate histology between ganglioneuroma and neuroblastoma
  - Most common in older children
  - Imaging resembles neuroblastoma
- Neuroblastoma
  - Malignant neoplasm associated with systemic symptoms
  - Most common in children less than 5 years old
  - Curvilinear and speckled calcification in 40%
  - May invade adjacent structures
Lymphoma
- Non-Hodgkin lymphoma is more common than Hodgkin disease in posterior compartment
- Enlarged lymph nodes or nodal mass, often displaying homogeneous soft tissue attenuation
- Necrosis is occasionally present, usually detected after contrast administration
Hiatal Hernia
- Superior herniation of stomach through esophageal hiatus
- May see air-fluid level on upright radiograph
Esophageal Tumor
- Carcinoma
  - Thickening of esophageal wall that is often eccentric
  - Luminal narrowing
  - Invasion of adjacent tissues
- Mesenchymal tumor
  - Most common histology is leiomyoma
  - Often asymptomatic
  - Margins are smooth

Helpful Clues for Less Common Diagnoses

Metastasis
- Often involves lymph nodes
- Involvement of posterior compartment lymph nodes is suggestive of primary malignancy within abdomen
Foregut Duplication Cyst
- Esophageal duplication cyst, bronchogenic cyst, neurenteric cyst
- Round or oval with smooth borders
- Thin wall with no enhancement; wall calcification is uncommon
- Cyst contents may be proteinaceous, with increased attenuation and increased signal on T1 MR images
- Neurenteric cysts are associated with adjacent vertebral anomalies
Extramedullary Hematopoiesis
- Associated with thalassemia, sickle cell anemia, and spherocytosis
- Multiple bilateral paraspinal masses
- Sharp borders with homogeneous attenuation
- May be associated with skeletal abnormalities
Aortic Aneurysm
- May involve aortic arch or descending aorta
- True aneurysm: Most commonly due to atherosclerotic disease
- False aneurysm: Most commonly due to trauma
Esophageal Varices
- Result of liver disease with chronic portal hypertension
- Vascular serpiginous masses within middle and posterior mediastinum
- Connect with azygos system to bypass portal drainage
Spine Mass
- Neoplasms: Myeloma, metastasis, primary bone tumor
- Infection: Spondylitis, paraspinous abscess
- Look for disc space and vertebral body destruction
- If mass is present, determine if it appears to arise from bone or soft tissues

Helpful Clues for Rare Diagnoses

Hemangioma
- Soft tissue mass
- Clue to diagnosis is internal phlebolith
- Appearance similar to soft tissue hemangiomas elsewhere in body
Lymphangioma
- Benign hyperplasia of lymphatic vessels
- Low-density mass that insinuates between adjacent structures
Meningocele
- Herniation of meninges beyond spinal canal
- Associated with neurofibromatosis and traumatic nerve root avulsion
- Direct communication with subarachnoid space around spinal cord
- Associated with adjacent vertebral anomalies in neurofibromatosis

Image Gallery

Axial NECT shows a soft tissue mass within the posterior mediastinum

that has expanded the right neural foramen

and extends into the central canal

Axial T1WI C+ FS MR in the same patient shows intense enhancement of the mass with several nonenhancing areas

. These areas represent cystic regions, a common finding with schwannomas.

(Left) Frontal radiograph shows mild levoscoliosis and a well-demarcated mediastinal soft tissue mass

. Note it does not silhouette with the descending thoracic aorta. (Right) Axial CECT in the same patient reveals a round homogeneous mass in the posterior mediastinum